The specific aims of this research are 1) to determine the pulmonary excretion rate of carbon monoxide (VECO) as an index of heme catabolism or total bilirubin formation (TBF) in premature or sick infants, 2) to study the relationship of VECO to carboxy-hemoglobin (COHb) and the factors governing this relationship and 3) to characterize the hormonal milieu at the time of birth in relation to postnatal TBF. Methodology includes determination of VECO using an open, flow-through hood collection system with modifications for studying subjects on ventilators and a gas chromatograph analyzer, utilizing a reduction gas detector with a CO resolution of (plus/minus) 1 part per billion, and other relevant measurements: COHb, serum vitamin E, in vitro hydrogen peroxide stress project incorporates and expertise of the pediatric subspecialties of neonatal-perinatal medicine, nutrition/metabolism, endocrinology and hematology as well as engineering and biochemistry. It utilizes the unique, noninvasive technique of trace gas analysis, which is well-suited for pediatric applications, especially studies involving infants. The importance of this research emanates from the specific aims which outline a multifaceted, highly integrated project, designed to address major gaps in our current knowledge regarding two very common problems in premature or sick infants related to postnatal heme catabolism: hyperbilirubinemia and anemia. Estimates of TBF in the first postnatal week will provide practical information about the magnitude of a major contributing factor to exaggerated neonatal jaundice in these subjects who are most at risk for injury related to bilirubin toxicity. Weekly estimates of TBF later in the postnatal period may reflect accurately red blood cell breakdown and thus can be used to assess antioxidant defense mechanisms in infants who are most at risk for hemolysis and anemia.